1. Field of the Invention
The invention relates to the art of removing toners from waste paper.
2. Description of the Prior Art
It is necessary to remove the ink from pulp fiber when processing waste paper for reuse. In the past these have been oil based inks which were removed by saponification reactions. There is, however, an increasing amount of waste paper which has been used as copy paper in an electrophotography process such as xerography or laser printing. These papers usually include synthetic resins and plasticizers, and normal deinking procedures and chemicals are not effective in removing these resins and plasticizers from the fibers and in separating them from the pulp.
In the art of xerography, an electrostatic latent image is formed by uniformly charging a photoconductive insulating surface on a xerographic plate followed by exposing the charged surface to a pattern of light. The latent image formed by this technique is then developed with electroscopic powder, also known as a toner, to form a powdered image which is then transferred to a sheet of normal bond paper. This powder image now contained on a paper is then fused into the paper to form a permanent reproduction of an original image. The usual toner powder is carbon black mixed with a styrene-acrylic copolymer as a binder.
One technique now in general use in developing xerographic images is cascade development. This technique is based on the phenomena of triboelectrification whereby upon bringing two similar materials into contact each material becomes electrically charged to a polarity opposite to that of the other. Thus, when the fine powdered toner is mixed with a relatively coarse beaded carrier, the toner particles become charged triboelectrically and cling to the surface of the carrier beads. Development of the electrostatic image is accomplished by falling or cascading the two component developer over the surface of the xerographic plate. As the beads, covered with toner, roll over the image, the electrostatic forces of the image overcome the carrier-toner bond and toner particles are deposited on the image areas. An example of the toner composition of this type is 25% polyvinylbutyral, 70% of a rosin modified phenol-formaldehyde and 5% carbon black. Patents disclosing these inks are Landrigan U.S. Pat. No. 2,753,308, Walkup et al. U.S. Pat. No. 2,638,416 and Grieg et al. U.S. Pat. No. 2,735,785.
One patent directed toward the removal of toners is Green U.S. Pat. No. 3,635,789. This is a two-step system in which the copy paper is repulped, diluted and agitated and the toner is skimmed from the surface. The pulp is transferred to a second tank and an immiscible organic liquid is added to the surface of the solution. The toner is again skimmed from the surface.
Fischer and Pfalzer Auslegeschrift No. 2,756,711 describes a process of deinking wastepaper by soaking the paper with a surface active material and treating it with terpene hydrocarbons or alcohols, aliphatic or aromatic hydrocarbons or alcohols, and collecting the ink on a calcium soap or magnesium soap accumulator. The accumulators may be calcium soap cones with pine oil. It was preferred, however, and the object of the Fischer, et al. invention to use less soap in the accumulator by absorbing the soap into the surface of a carrier material and using this as the accumulator. The materials used as the carriers for the soap have large specific surfaces. Examples are groundwood, sawdust, porous plastic particles and bark waste. In place of calcium or magnesium soap, oleic acid may be absorbed on the surface and then be saponified with lime. Other chemicals such as amines, petroleum or glycol esters may be used in place of the calcium soap.
Miyamoto et al. U.S. Pat. No. 3,764,460 discloses a deinking process in which the paper is pulped in an aqueous system containing a polyolefin dispersed or emulsified in micro-fine particles with a surface active agent such as a dispersing agent or emulsifier. The printing inks are desorbed from the printed paper and absorbed on the polyolefin particles which are then isolated from the system. It is helpful in isolating the waste to add organic solvents, emulsions containing the solvents, clays or water soluble salts capable of dissociating the di- or polyvalent metal cation in water.
Both of these patents are also discussed in Puddington U.S. Pat. No. 4.076,578. The process in this latter patent again requires forming a pulp, precipitating any ink dispersing agent present in the pulp and agitating the resulting aqueous mixture in the presence of inserted selected non-soap collecting solids and collecting ink solids on the surface of the collecting solids. The collecting solids are selected from materials having hydrophobic surfaces with a strong affinity for the ink particles such as waxes, polyolefins and other vinyl polymers, rubber, e.g. ground waste rubber, solid petroleum materials, pitches, gums, sulfur, silica with surface hydroxyls replaced with hydrophobic organic groups, etc. If the collecting surface has insufficient attraction for retention of ink particles, the surface is coated with a hydrophobic adhesive collecting agent. These agents would include sticky viscous oils, soft waxes, sticky gums and hydrophobic contact adhesives in small amounts.
One method to remove toner proposed by DeSoto, Inc. is to treat the copy paper at 4-5% consistency with 2-3% caustic and 1-2% surfactant DeSoInk #652. The amount of caustic and DeSoInk is based on the weight of the paper. The time of the treatment is 15-20 minutes and the temperature 160.degree.-170.degree. F. The toner is supposed to form into balls and be removed by centrifuging and reverse centrifuging. It has been found, however, that this method requires a heavy coating of toner to be effective. It is not effective in removing substantially all of the toner if the paper is covered with only a light or averge amount of toner.